Mould and Mildew

I was at a party the other day and I mentioned that I had done some work
studying fungi at university, and somebody asked
me the other day. "what kind of fungus is it that grows on shower tiles?", "is
it really a fungus? is Mould different from Mildew?".
Well, I had always assumed that yes it was a fungus, and that mildew was a
symptom of mould growth...but I checked through a couple of mycology books and
couldn't find anything definitive and ran a couple of checks on some CD-Rom
references at the university and couldn't find anything...
I suppose I could always take a scraping and have a look under the microscope
but I just never seem to get around to it..
Does anybody have any names or id's on shower tile mould?
Sincerely,
R. Gibson